A patient's blood pressure is measured in almost all cases using a sphygmomanometer, or blood pressure cuff. This term refers to a device consisting of an inflatable bladder housed within a sleeve (cuff) and connected to a manometer. The cuff is wrapped around the patient's upper arm and the bladder inflated to restrict blood flow through the patient's brachial artery. The manometer is used to read the pressure at which the blood flow first resumes (known as the systolic blood pressure, or SBP) and the pressure at which the blood flow becomes unimpeded (known as the diastolic blood pressure, or DBP). These occurrences may be identified manually using a stethoscope (to listen for the appearance and disappearance of the Korotkoff sounds), or digitally using electronic calculation.
Currently, the typical blood pressure cuff is sized for a range of arm circumferences yet contains a bladder of fixed width. This is true despite the fact that the SBP and the DBP read by the manometer vary as the ratio of bladder width to arm circumference varies. As a result, any patient whose arm circumference does not fall at the center of the range corresponding to a given cuff size will receive an inaccurate blood pressure measurement. In an attempt to mitigate this problem, the American Heart Association (AHA) has recommended using seven different cuff sizes (corresponding to seven different ranges of arm circumference) for patients ranging from pediatric to large adult. Because each cuff size contains a fixed-width bladder, however, even using the appropriately sized cuff can result in up to a plus or minus 5% error in blood pressure readings. Furthermore, because following the AHA recommendation requires measuring the patient's arm before choosing the appropriate cuff size, many practitioners (for example in clinics, wards, and/or physicians' offices) ignore the recommendation and use a standard cuff with a 12-centimeter-wide bladder in almost all blood pressure measurements. This can result in even larger errors, on the order of 5-10 mm Hg in some tests, for both the SBP and the DBP. Such errors can lead to costly misdiagnoses, especially for patients whose blood pressures are near the cutoff levels for prescribing treatment for hypertension. Further, with cutoff levels used to prescribe hypertension medication, errors in blood pressure measurements that result in high blood pressure measurements may result in patients receiving medication who do not need the medication. This results in increased costs and patients being unnecessarily medicated. Errors in blood pressure measurements that result in low blood pressure measurements may result in patients that should receive blood pressure medication not receiving such medication, thereby resulting in health complications due to untreated hypertension.
It has been suggested that the ratio of the width of the bladder covering the artery to the patient's arm circumference should be approximately in the range of 40% in order to properly occlude the artery. In addition, it has been suggested that the bladder should encircle at least about 80% of the arm and less than 100% of the arm (such that the bladder does not overlap onto itself) in order to provide accurate readings. Based on the above discussion of current practices, there exists a need for a blood pressure cuff that meets both of these requirements for accuracy while fitting patients with a range of arm circumferences.